fix(imports): break models<->dag_engine circular dependency

Track.get_executable_tickets (in models.py) called TrackDAG at
runtime, forcing a top-level import of src.dag_engine into models.py
and creating a 2-cycle that broke whichever module loaded second
(Ticket was not yet defined when models.py loaded first; TrackDAG
was not yet defined when dag_engine.py loaded first).

Fix: hoist the method out of the Track dataclass and into a free
function get_executable_tickets(track) in dag_engine.py. models.py
no longer needs TrackDAG at all, so the cycle is one-directional
(models -> dag_engine) and resolves cleanly in any import order.

Tests updated:
- tests/test_mma_models.py: import get_executable_tickets and call
  it instead of track.get_executable_tickets() (4 call sites)
- tests/test_conductor_engine_v2.py: comment update

Verified both import orders resolve cleanly:
  forward:  import src.models; import src.dag_engine  -> OK
  reverse:  import src.dag_engine; import src.models  -> OK
34 tests pass (test_mma_models, test_dag_engine, test_execution_engine,
test_arch_boundary_phase3, test_track_state_schema).

src/dag_engine.py

@@ -89,7 +89,7 @@ class TrackDAG:
   Returns a list of tickets that are in 'todo' status and whose dependencies are all 'completed'.
   Returns:
   A list of Ticket objects ready for execution.
-  [C: src/models.py:Track.get_executable_tickets, tests/test_dag_engine.py:test_get_ready_tasks_branching, tests/test_dag_engine.py:test_get_ready_tasks_linear, tests/test_dag_engine.py:test_get_ready_tasks_multiple_deps, tests/test_orchestration_logic.py:test_track_executable_tickets]
+  [C: src/dag_engine.py:get_executable_tickets, tests/test_dag_engine.py:test_get_ready_tasks_branching, tests/test_dag_engine.py:test_get_ready_tasks_linear, tests/test_dag_engine.py:test_get_ready_tasks_multiple_deps, tests/test_orchestration_logic.py:test_track_executable_tickets]
   """
   ready = []
   for ticket in self.tickets:
@@ -162,6 +162,17 @@ class TrackDAG:
     raise ValueError("Dependency cycle detected")
    return result
 
+def get_executable_tickets(track: "Track") -> List[Ticket]:
+ """
+ Convenience: returns the ready-to-execute tickets of a Track.
+ Free function (instead of Track.get_executable_tickets) so that
+ src/models.py does not need to import TrackDAG at module level,
+ breaking the models<->dag_engine circular dependency.
+ [C: tests/test_mma_models.py:test_track_get_executable_tickets, tests/test_mma_models.py:test_track_get_executable_tickets_complex]
+ """
+ return TrackDAG(track.tickets).get_ready_tasks()
+
+
 class ExecutionEngine:
  """
  A state machine that governs the progression of tasks within a TrackDAG.

src/models.py

@@ -341,16 +341,8 @@ class Track:
  description: str
  tickets:     List[Ticket] = field(default_factory=list)
 
- def get_executable_tickets(self) -> List[Ticket]:
-  """
-  [C: tests/test_mma_models.py:test_track_get_executable_tickets, tests/test_mma_models.py:test_track_get_executable_tickets_complex]
-  """
-  dag = TrackDAG(self.tickets)
-  return dag.get_ready_tasks()
-
  def to_dict(self) -> Dict[str, Any]:
   """
-  [C: src/personas.py:PersonaManager.save_persona, src/presets.py:PresetManager.save_preset, src/project_manager.py:save_project, src/project_manager.py:save_track_state, src/tool_presets.py:ToolPresetManager.save_bias_profile, src/tool_presets.py:ToolPresetManager.save_preset, src/workspace_manager.py:WorkspaceManager.save_profile, tests/test_bias_models.py:test_bias_profile_model, tests/test_bias_models.py:test_tool_model, tests/test_bias_models.py:test_tool_preset_extension, tests/test_context_presets_models.py:test_context_preset_serialization, tests/test_context_presets_models.py:test_file_view_preset_serialization, tests/test_custom_slices_annotations.py:test_file_item_custom_slices_round_trip_annotations, tests/test_custom_slices_annotations.py:test_file_item_custom_slices_serialization_with_annotations, tests/test_event_serialization.py:test_user_request_event_serialization, tests/test_external_editor.py:TestExternalEditorConfig.test_to_dict, tests/test_external_editor.py:TestTextEditorConfig.test_to_dict, tests/test_file_item_model.py:test_file_item_to_dict, tests/test_gui_events_v2.py:test_user_request_event_payload, tests/test_history_manager.py:TestHistoryManager.test_snapshot_roundtrip, tests/test_mcp_config.py:test_mcp_configuration_to_from_dict, tests/test_mcp_config.py:test_mcp_server_config_to_from_dict, tests/test_per_ticket_model.py:test_model_override_serialization, tests/test_persona_id.py:test_ticket_persona_id_serialization, tests/test_persona_models.py:test_persona_defaults, tests/test_persona_models.py:test_persona_serialization, tests/test_slice_editor_behavior.py:test_add_slice_with_annotations, tests/test_thinking_gui.py:test_thinking_segment_model_compatibility, tests/test_ticket_queue.py:test_ticket_to_dict_priority, tests/test_tiered_aggregation.py:test_persona_aggregation_strategy, tests/test_track_state_schema.py:test_track_state_to_dict, tests/test_track_state_schema.py:test_track_state_to_dict_with_none, tests/test_ui_summary_only_removal.py:test_file_item_serialization_with_flags]
   """
   return {
    "id":          self.id,
@@ -361,7 +353,6 @@ class Track:
  @classmethod
  def from_dict(cls, data: Dict[str, Any]) -> "Track":
   """
-  [C: src/personas.py:PersonaManager.load_all, src/presets.py:PresetManager.load_all, src/project_manager.py:load_project, src/project_manager.py:load_track_state, src/tool_presets.py:ToolPresetManager.load_all_bias_profiles, src/tool_presets.py:ToolPresetManager.load_all_presets, src/workspace_manager.py:WorkspaceManager.load_all_profiles, tests/test_bias_models.py:test_bias_profile_model, tests/test_bias_models.py:test_tool_model, tests/test_bias_models.py:test_tool_preset_extension, tests/test_context_presets_models.py:test_context_preset_from_dict_legacy, tests/test_context_presets_models.py:test_context_preset_serialization, tests/test_context_presets_models.py:test_file_view_preset_serialization, tests/test_custom_slices_annotations.py:test_file_item_custom_slices_deserialization_with_annotations, tests/test_custom_slices_annotations.py:test_file_item_custom_slices_round_trip_annotations, tests/test_external_editor.py:TestExternalEditorConfig.test_from_dict_with_dict_editors, tests/test_external_editor.py:TestExternalEditorConfig.test_from_dict_with_string_editors, tests/test_external_editor.py:TestTextEditorConfig.test_from_dict_with_diff_args, tests/test_external_editor.py:TestTextEditorConfig.test_from_dict_without_diff_args, tests/test_file_item_model.py:test_file_item_from_dict, tests/test_file_item_model.py:test_file_item_from_dict_defaults, tests/test_history_manager.py:TestHistoryManager.test_snapshot_roundtrip, tests/test_mcp_config.py:test_mcp_configuration_to_from_dict, tests/test_mcp_config.py:test_mcp_server_config_to_from_dict, tests/test_per_ticket_model.py:test_model_override_default_on_deserialize, tests/test_per_ticket_model.py:test_model_override_deserialization, tests/test_persona_id.py:test_ticket_persona_id_deserialization, tests/test_persona_models.py:test_persona_defaults, tests/test_persona_models.py:test_persona_deserialization, tests/test_project_serialization.py:TestProjectSerialization.test_backward_compatibility_strings, tests/test_slice_editor_behavior.py:test_add_slice_with_annotations, tests/test_ticket_queue.py:test_ticket_from_dict_default_priority, tests/test_ticket_queue.py:test_ticket_from_dict_priority, tests/test_tiered_aggregation.py:test_persona_aggregation_strategy, tests/test_track_state_schema.py:test_track_state_from_dict, tests/test_track_state_schema.py:test_track_state_from_dict_empty_and_missing, tests/test_ui_summary_only_removal.py:test_file_item_serialization_with_flags]
   """
   return cls(
    id          = data["id"],
@@ -938,8 +929,6 @@ class MCPServerConfig:
 
 #endregion: MCP Config
 
-from src.dag_engine import TrackDAG
-
 @dataclass
 class MCPConfiguration:
  mcpServers: Dict[str, MCPServerConfig] = field(default_factory=dict)